A TDMA/TDD system provided by combining TDMA (Time Division Multiple Access) and TDD (Time Division Duplex) is adopted as a wireless access system of a digital mobile telephone system, a PHS system, etc. Further, in addition to the TDMA/TDD system, an OFDMA (Orthogonal Frequency Division Multiplexing Access) system making the most of OFDM (Orthogonal Frequency Division Multiplexing) is proposed.
The OFDMA system is a system of dividing a carrier wave for modulating data into “subcarriers” (subdivided carrier waves) orthogonal to each other, distributing a data signal into the subcarriers, collecting subcarriers from among the subcarriers into a group, assigning one or more groups to each user, and conducting multiplex communication. Each of the groups is called a subchannel. This means that each user conducts communications using one or more assigned subchannels. The number of subchannels is increased or decreased adaptively for assignment in response to the data amount, the propagation environment, etc., for conducting communications.
An adaptive array technology using an adaptive array exists to perform transmission and reception having directivity at the transmitting time of a down signal from a base station to a terminal and at the receiving time of an up signal from a terminal by a base station to suppress the effect of communications in a different base station and maintain good communication quality.
Signal processing with an adaptive array extracts precisely a signal from any desired terminal by calculating a weight vector (reception weight vector) made of a reception coefficient (weight) for each antenna of a base station based on a reception signal from a terminal and performing adaptive control, namely, multiplying the reception signals of a plurality of antennas by each element of the reception weight vector.
As the processing is performed, the up signal from the antenna of each terminal is received by an adaptive array antenna of the base station and is separated and extracted with reception directivity.
Further, a signal provided by multiplying a transmission signal by each element of a transmission weight vector calculated based on the reception weight vector is output from each of antennas, whereby a down signal from the base station to the terminal is transmitted with transmission directivity for the antenna of the terminal (refer to patent literature 1).    Patent Literature 1: JP-A-2003-283411 (paragraphs [0005] and [0006])